1. Field of the Invention
The present invention relates generally to endoscopic surgical instruments. More particularly, the invention relates to an endoscopic surgical instrument having end effectors made out of a combination of conductive and non-conductive materials. The invention has particular use with respect to bipolar endoscopic cautery. For purposes herein, the term "endoscopic instruments" is to be understood in its broadest sense and to include laparoscopic, arthroscopic, and neurological instruments, as well as instruments which are inserted through an endoscope, although it is not limited thereto.
2. State of the Art
Endoscopic surgery is widely practiced throughout the world today and its acceptance is growing rapidly. In general, endoscopic/laparoscopic surgery involves one or more incisions made by trocars where trocar tubes are left in place so that endoscopic surgical tools may be inserted through the tubes. A camera, magnifying lens, or other optical instrument is often inserted through one trocar tube, while a cutter, dissector, or other surgical instrument is inserted through the same or another trocar tube for purposes of manipulating and/or cutting the internal organ. Sometimes it is desirable to have several trocar tubes in place at once in order to receive several surgical instruments. In this manner, organ or tissue may be grasped with one surgical instrument, and simultaneously may be cut with another surgical instrument; all under view of the surgeon via the optical instrument in place in the trocar tube.
Various types of endoscopic surgical instruments are known in the art. One type of instrument generally comprises a slender tube containing a push rod which is axially movable within the tube by means of a handle or trigger-like actuating means. An end effector is provided at the distal end of the tube and is coupled to the push rod by means of a clevis so that axial movement of the push rod is translated to rotational or pivotal movement of the end effector. End effectors may take the form of scissors, grippers, cutting jaws, forceps, and the like. Because of their very small size and the requirements of strength and/or sharpness, end effectors are difficult to manufacture and are typically formed of forged stainless steel, or are cast from bronze or from a superalloy.
Modern endoscopic procedures often involve the use of electrocautery, as the control of bleeding by coagulation during surgery is critical both in terms of limiting loss of blood and in permitting a clear viewing of the surgical site. As used herein, cautery, electrocautery, and coagulation are used interchangeably. Several types of electrocautery devices for use in endoscopic surgery are described in the prior art. Monopolar electrosurgical instruments employ the instrument as an electrode, with a large electrode plate beneath and in contact with the patient serving as the second electrode. High frequency voltage spikes are passed through the instrument to the electrode (i.e., end effector) of the endoscopic instrument to cause an arcing between the instrument and the proximate tissue of the patient. The current thereby generated continues through the patient to the large electrode plate beneath the patient. Monopolar cautery has the disadvantage that the current flows completely through the patient. Because control of the current path through the body is not possible, damage can occur to tissue both near and at some distance from the surgical site. In addition, it has been observed that monopolar cautery can result in excessive tissue damage due to the arcing between the end effector and the tissue.
In order to overcome the problems associated with monopolar cautery instruments, bipolar instruments have been introduced. In bipolar electrosurgical instruments, two electrodes which are closely spaced together are utilized to contact the tissue. Typically, one end effector acts as the first electrode, and the other end effector acts as the second electrode, with the end effectors being electrically isolated from each other and each having a separate current path back through to the handle of the instrument. Thus, in a bipolar instrument, the current flow is from one end effector electrode, through the tissue to be cauterized, to the other end effector electrode.
Various endoscopic instruments with cautery capability are known in the art. Several hemostatic bipolar electrosurgical scissors have also been described. U.S. Pat. No. 3,651,811 to Hildebrandt describes a bipolar electrosurgical scissors having opposing cutting blades forming active electrodes. The described scissors enables a surgeon to sequentially coagulate the blood vessels contained in the tissue and then to mechanically sever the tissue with the scissor blades. In particular, with the described bipolar electrosurgical scissors, the surgeon must first grasp the tissue with the scissor blades, energize the electrodes to cause hemostasis, de-energize the electrodes, and then close the scissor blades to sever the tissue mechanically. The scissors are then repositioned for another cut accomplished in the same manner. With the bipolar electrosurgical scissors of Hildebrandt, the surgeon cannot maintain the electrodes in a continuously energized state because the power supply would be shorted out and/or the blades damaged if the blades are permitted to contact each other while energized.
The disadvantages of the bipolar scissors of Hildebrandt are overcome by the disclosure in U.S. Pat. Nos. 5,324,289 and 5,330,471 to Eggers. In its preferred embodiment, the bipolar electrosurgical scissors of Eggers comprise a pair of metal scissor blades which are provided with an electrically insulating material interposed between the shearing surfaces of the blades so that when the scissor blades are closed, the metal of one blade never touches the metal of the other blade; i.e., the insulating material provides the cutting edge and the shearing surface. With the arrangement provided by Eggers, a cautery current will pass from the top back edge of the bottom metal blade through the tissue which is to be cut and to the bottom back edge of the top metal blade directly in advance of the cutting action. As the scissors are gradually closed, the hemostasis preferentially occurs at a location just in advance of the cutting point which itself moves distally along the insulated cutting edges of the blades in order to sever the hemostatically heated tissue. With this arrangement, the scissors may be maintained in a continuously energized state while performing the cutting. The Eggers patent describes various alternative embodiments of the bipolar scissors, including the use of metal blades with only one blade being insulated on its shearing surface, and the use of insulating blades with back surfaces coated with metal.
The disadvantage of scissor blades which have non-conductive cutting edges and shearing surfaces is that they are difficult to operate. The non-conductive surfaces are relatively non-lubricous and do not have the smooth operation and feel of a metal on metal cutting/shearing action. Parent application Ser. No. 08/429,596 discloses scissor blades comprised of an electrically conductive electrode, an electrically insulating material, and a coating of titanium dioxide, chromium dioxide, or zirconium dioxide, where the coating provides a lubricious surface which simulates a metal on metal feel. In one embodiment, the electrode layer is a metal blade which is typically constructed from stainless steel, while the insulating layer is an alumina ceramic which is deposited, bonded, or otherwise fixed on the metal blade, and a titanium dioxide coating is deposited, bonded, or otherwise fixed onto the ceramic and provides the cutting edge and shearing surface. In another embodiment, the electrode layer of the scissor blades is a metal blade, and the titanium dioxide is mixed with the alumina ceramic and then applied directly to the conductive electrode. In this preferred embodiment, the ratio by weight of alumina ceramic to titanium dioxide is 87/13, although the ratio can range from 75/25 to 95/5 and still provide the desired insulation and lubricity. In a third embodiment of the invention, the insulating layer is a ceramic support, with the electrode layer and the titanium dioxide shearing surface layer being deposited, bonded, or otherwise fixed to opposite sides of the ceramic support. In all embodiments, since the coated cutting edges and preferably at least a portion of the shearing surfaces are insulated from the electrodes, no short circuit can form between the electrodes even though the cutting edge and shearing surface of each scissor blade are in contact with the cutting edge and shearing surface of the other scissor blade.
In the prior art, as well as in the parent application hereto, a cross sectional profile of an endoscopic scissor blade generally defines an included angle of between 60-90.degree. at the cutting edge. This may be seen in the prior art Figures of 1 and 1a where the blades 26, 28 have an included angle .alpha. of approximately 70.degree. at their cutting edges 26b, 28b. It is generally believed in the art that the cutting edge of a surgical scissor blade, and in particular an endosurgical scissor blade, must be defined by an angle of no more than 90.degree. in order to achieve effective cutting.
U.S. Pat. No. 4,709,480 to Takigawa et al. disclosed a scissors for use in horticulture and for industrial purposes. Prior art FIG. 1b shows a cross section of the scissors which has one metallic cutting blade 11 and one ceramic cutting blade 12. Takigawa et al. teaches that if the cutting edge of a ceramic cutting blade is defined by an acute included angle, the ceramic is likely to be damaged. The inventors herein have confirmed that this is also true in the case of endoscopic scissors. According to Takigawa et al., the damage to the ceramic blade is most likely to be caused by the blades interfering with each other as the bow in the scissor blade causes their respective cutting edges to press against each other at a single moving point of contact as the blades are closed. The solution proposed by Takigawa et al. is to locate the cutting edge of the ceramic blade away from the shearing surface so that it never touches the cutting edge of the metallic blade. Thus, the cutting edge of the ceramic blade disclosed by Takigawa et al., as shown in prior art FIG. 1b, is defined by an adjacent side 16 which forms an obtuse angle .theta..sub.2 with the shearing surface 15 and a beveled side 17. While Takigawa et al. does not specifically disclose what angle is formed by the adjacent side 16 and the beveled side 17 (i.e. the included angle of the cutting edge), it appears to be close to 90.degree.. The scissors proposed by Takigawa et al. may have utility in horticulture and in some industrial applications. However, they are unsuitable for surgical procedures. As those skilled in the art will appreciate from prior art FIG. 1b, when the scissors are used to cut article "c", the cutting edge of the metallic blade 11 will attempt to sever the article along a virtual plane A-B. Since the cutting edge of the ceramic blade 12 is not located in the plane A-B, it will pull the article c up and away from the plane A-B. Thus, depending on the nature of the article c, it may be torn apart rather than cut. Scissors of this design would certainly tear, rather than sever, human tissue.